(501a) Liquid Hot Water Pretreatment of Lignocellulosic Biomass to Enhance Sugar Recovery and Enzymatic Digestibility of Cellulose

Several processes are required in cellulosic ethanol production from lignocellulosic feedstocks such as pretreatment, enzymatic hydrolysis, fermentation, and product separation/ distillation. The native lignocellulosic biomass has limited its accessibility to enzymes and microorganisms due to its complex cell wall structure of cellulose-hemicellulose-lignin. Therefore, pretreatment is an essential prerequisite to overcome recalcitrance of biomass and enhance the bio-chemical conversion ratio of polysaccharides.An effective pretreatment can reduce the downstream pressure by making cellulose more accessible to the enzymes and minimize the formation of degradation products that inhibit the growth of fermentative microorganisms. For the advantages of without additional chemicals, less inhibitory products and higher pentosan recovery, liquid hot water pretreatment become attractive.

The process of step-change flow rate (SCF) liquid hot water pretreatment and step-change temperature (SCT) liquid hot water pretreatment were developed in GIEC, respectively, for the sweet sorghum bagasse (SSB) and eucalyptus wood chips (EWC) to enhance sugar recovery and enzymatic digestibility of cellulose. Furthermore, the decomposition mechanism of hemicellulose and lignin in the liquid hot water was investigated.

  Moreover, different structural changes at the plant tissue, cellular, and cell wall levels were investigated to understand the decomposition mechanism of sugarcane bagasse cell wall in the liquid hot water pretreatment. The transmission electron microscopy (TEM) images showed that sugarcane bagasse cell walls were composed of the middle lamella (ML) layers, the primary wall (P) layers, and the secondary wall layers. While after the pretreatment, the boundaries among the S1, S2 and S3 layers in the secondary wall of treated samples could not be distinguished exactly. The data from the scanning electron microscopy and energy dispersive X-ray analysis(SEM-EDXA)shows that the migration of lignin happens among different cell wall layers. Moreover, pseudo-lignin, the degradation products of lignin and xylan, appeared on the surface of pretreated sugarcane bagasse. Furthermore, Raman spectra of treated sugarcane bagasse indicated that the distribution of cellulose in the cell wall was homogenized, and the difference in the chemical composition was reduced. All of these changes on the ultrastructural level of the cell wall were responsible for the improvement of the enzymatic digestibility of treated samples.